No detectable cytomegalovirus and Epstein-Barr virus genomes in the pancreas of recent-onset IDDM patients

Type I diabetes mellitus: genetic factors and presumptive enteroviral etiology or protection

We review type 1 diabetes and host genetic components, as well as epigenetics and viruses associated with type 1 diabetes, with added emphasis on the enteroviruses, which are often associated with triggering the disease. Genus Enterovirus is classified into twelve species of which seven (Enterovirus A, Enterovirus B, Enterovirus C, and Enterovirus D and Rhinovirus A, Rhinovirus B, and Rhinovirus C) are human pathogens. These viruses are transmitted mainly by the fecal-oral route; they may also spread via the nasopharyngeal route. Enterovirus infections are highly prevalent, but these infections are usually subclinical or cause a mild flu-like illness. However, infections caused by enteroviruses can sometimes be serious, with manifestations of meningoencephalitis, paralysis, myocarditis, and in neonates a fulminant sepsis-like syndrome. These viruses are often implicated in chronic (inflammatory) diseases as chronic myocarditis, chronic pancreatitis, and type 1 diabetes. In this review we discuss the currently suggested mechanisms involved in the viral induction of type 1 diabetes. We recapitulate current basic knowledge and definitions.

Viral infections as potential triggers of type 1 diabetes

During the last decades, the incidence of type 1 diabetes (T1D) has increased significantly, reaching percentages of 3% annually worldwide. This increase suggests that besides genetical factors environmental perturbations (including viral infections) are also involved in the pathogenesis of T1D. T1D has been associated with viral infections including enteroviruses, rubella, mumps, rotavirus, parvovirus and cytomegalovirus (CMV). Although correlations between clinical presentation with T1D and the occurrence of a viral infection that precedes the development of overt disease have been recognized, causalities between viruses and the diabetogenic process are still elusive and difficult to prove in humans. The use of experimental animal models is therefore indispensable, and indeed more insight in the mechanism by which viruses can modulate diabetogenesis has been provided by studies in rodent models for T1D such as the biobreeding (BB) rat, nonobese diabetic (NOD) mouse or specific transgenic mouse strains. Data from experimental animals as well as in vitro studies indicate that various viruses are clearly able to modulate the development of T1D via different mechanisms, including direct beta-cell lysis, bystander activation of autoreactive T cells, loss of regulatory T cells and molecular mimicry. Data obtained in rodents and in vitro systems have improved our insight in the possible role of viral infections in the pathogenesis of human T1D. Future studies will hopefully reveal which human viruses are causally involved in the induction of T1D and this knowledge may provide directions on how to deal with viral infections in diabetes-susceptible individuals in order to delay or even prevent the diabetogenic process.

A proposal of three distinct subtypes of type 1 diabetes mellitus based on clinical and pathological evidence

To better understand the pathogenesis of type 1 diabetes, our group performed a pathological examination on the pancreas tissue of recent-onset type 1 diabetics and analysed their clinical characteristics. These studies led us to speculate that there are three distinct subtypes of type 1 diabetes mellitus: autoimmune, nonautoimmune fulminant and nonautoimmune nonfulminant (or nonautoimmune chronic). The autoimmune type 1 diabetes mellitus comprises about 60% of the patients and is characterized by insulitis and over-expression of class I MHC molecules in the islet cells, a high prevalence of diabetes-related autoantibodies, and a progressive loss of beta-cell function after the onset of diabetes. The nonautoimmune nonfulminant type 1 diabetes mellitus includes about 30% of the patients, shows neither insulitis nor over-expression of class I MHC antigen in the islet cells, and has a low prevalence of diabetes-related autoantibodies and a relatively slow progression of beta-cell loss after the onset of diabetes. The nonautoimmune fulminant type 1 diabetes comprises about 10% of patients and shows neither insulitis nor over-expression of class I MHC molecules, but is characterized by lymphocytic infiltration in the exocrine pancreatic tissue, elevated serum pancreatic enzyme levels, absence of diabetes-related autoantibodies and a remarkably aggressive course of disease. The appropriate classification of type 1 diabetes would increase our understanding of the pathogenesis of the disease and would allow to develop therapeutic means based on this understanding.

Insulin-Dependent Diabetes Mellitus: Islet Changes in Relation to Etiology and Pathogenesis

Type and type II diabetes are the most common types of diabetes. The ratio of type I to type II diabetes is about 1:9. Type I diabetes is caused by absolute insulin deficiency and is therefore referred to as insulin-dependent diabetes. The disease becomes manifest clinically in childhood or adolescence ("juvenile diabetes"), though onset in adulthood is increasingly being observed. Morphologically a subtotal (>80%) to total loss of B-cells in the pancreatic islets occurs. Lymphocytic insulitis, which disappears after the B-cells have been totally destroyed, is pathogneumonic of type I diabetes. This insulitis is an expression of an autoimmune event that is triggered by a multitude of factors. An important factor appears to be a genetic predisposition (human leukocyte antigen [HLA] DR3/DR4/DQ8) in connection with as-yet-unknown environmental factors (e.g., viruses). Autoantibodies, such as islet cell cytoplasmic antibodies (ICA). insulin autoantibodies (IAA) and/or autoantibodies to the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid carboxylase (GAD), are already detectable in a prediabetic phase, though it is not possible to predict the time of clinical onset. The course of the disease is dependent on age. Young children require insulin therapy sooner than juveniles or adults.

Mitochondrial DNA mutations in pancreatic biopsy specimens from IDDM patients

We investigated the contribution of mitochondrial DNA mutations to the pathogenesis of IDDM by analyzing mitochondrial DNA in pancreatic biopsy specimens and peripheral blood cells from 18 patients with newly-diagnosed IDDM. All patients presented with typical abrupt onset of diabetes and ketosis on initial examination. Point mutations at nucleotides 3243, 3271 and 8344 were assayed by polymerase chain reaction and restriction fragment length polymorphism analysis or by mismatch-primer analysis. A common large deletion from nucleotides 8483-13459 was analyzed by a primer shift method. All of these mutations are known to be pathogenic mutations. However, none of the mitochondrial DNA mutations were detected in any of 18 IDDM patients. Several types of mitochondrial DNA mutation have been identified in the peripheral blood cells in some patients with non-insulin-dependent diabetes mellitus as well as in some with IDDM, however, our results suggest that abrupt-onset IDDM does not correlate with any of the known mitochondrial DNA mutations.